Hydrocarbons can be transferred from a pipeline at the sea floor to a vessel by transfer systems such as the CALM (catenary anchor leg mooring) type which includes a buoy anchored by several chains and tied by a hawser to the vessel. A flexible hose can extend up from the sea floor pipeline to the buoy, and another flexible hose can extend from a fluid swivel on the buoy and along the water to the vessel. Such an installation could be utilized to transfer cooled liquified gas, except that it is difficult to construct a reliable flexible hose that can lie in the water and carry such a product.
LPG (liquified petroleum gas) can be cooled to a temperature such as -45.degree. C. to reduce its volume to perhaps 1/400th its volume as a gas at atmospheric pressure. Actually, LPG is liquid at -43.degree. C. and atmospheric pressure, and at 154 psi and ambient temperature. A flexible hose which has been used on land to carry LPG includes walls formed of multiple layers of rubber and steel wire, and also includes microscopic passages extending through part of the wall thickness to enable the bleeding out of vapor. It has been found that when LPG is pumped through the hose, small droplets of the liquid penetrate into the walls of the hose, into minute cracks and the like. Such penetration occurs because typical LPG has a very low surface tension which enables it to penetrate deeply into capillary tube-like passages. When the small droplets later expand, especially when the flow of LPG stops and the temperature of the hose rises, the volume of the droplets expands many times as it vaporizes. For example, at a pressure of perhaps 100 psi at which LPG may be pumped, the vapor has a volume about 60 times that of the liquid, and at atmospheric pressure has a volume of about 400 times as great. Without the presence of microscopic passages to permit the rapid bleeding out of the vapor, the vapor bubbles form blisters in the hose, which weakens it and eventually requires hose replacement.
While the bleedable hose can be used to carry LPG on land where the hose is surrounded by air, difficulties can arise if such a hose is used in water. When the above-described flexible hose is utilized in water, then water may enter the outer ends of the bleed passages when the hose does not carry LPG. When LPG again flows through the hose and it cools, the water in the bleed passages freezes, and in freezing expands and becomes tightly locked in place. The bleed passages are blocked, and cannot vent the vapor. A flexible hose which could lie in the water and carry LPG without damage to the hose by interaction with the water, would be of great value in the transportation of LPG as to a vessel moored offshore.